1. Field of the Invention
The present invention relates to an air passage controlling system for opening and closing an air passage and for adjusting an amount of air flowing through the air passage by moving a film door. The air passage controlling system is used for selecting an air outlet mode of an air conditioning apparatus, and is used for mixing air in the air conditioning apparatus.
2. Related Art
In a conventional air conditioning apparatus for a vehicle, air introduced from a blower unit passes through an evaporator or a heater core disposed in an air duct, and is blown toward a passenger compartment from air outlets in the passenger compartment through each opening formed on the air duct. To simplify a control for opening and closing each opening of the air duct, an air passage controlling system having a film door is described in JP-A-6-74548.
In the air passage controlling system, as shown in FIG. 10, a film door 1 has a plurality of film openings la, and is moved in a longitudinal direction of the film door 1. One end of the film door 1 is wound around a driving shaft 2, and the other end thereof is wound around a driven shaft 3. The film door 1 is disposed to move along an air duct 4 having a plurality of openings 5 (partially shown in FIG. 10). The driving shaft 2 is rotated by a step motor 6 controlled according to pulse signals sent from a microcomputer. When the driving shaft 2 is rotated, the film door 1 is moved by or wound around the driving shaft 2 so that the film openings la of the film door 1 are stopped at a predetermined position on the air duct 4.
In this system, however, because the step motor 6 is expensive, a price of the system tends to be high, although the system has an excellent accuracy in stoppage. Further, because the system does not have a position detector for detecting a position of the film door 1, an initialization operation for returning the film door 1 to an original position is performed whenever the system is used.
To solve the above-mentioned problem, a servomotor including a potentiometer may be used instead of the step motor 6. However, because the maximum detectable rotation angle for the servomotor is approximately 180xc2x0 while the driving shaft 2 rotates at over 360xc2x0 (e.g., three rotations), a reduction intermediate gear is required between the driving shaft 2 and the servomotor. This results in increase of a size and a cost of the air passage controlling system.
In view of the foregoing problems, it is an object of the present invention to provide an air passage controlling system which opens and closes an air passage and adjusts an amount of air flowing through the air passage by moving a film door at a predetermined position, without increasing production cost.
According to the present invention, an air passage controlling system includes a film member having a film opening, first and second shafts for moving the film member therebetween, an electric motor for rotating the first shaft member, and a potentiometer, rotatable in multiple, for detecting a rotation angle of the first shaft. The electric motor is controlled by a controlling unit according to a rotation angle of the first shaft, detected by the potentiometer. Because the potentiometer can detect the rotation angle of the first shaft even if the rotation angle of the first shaft is more than 360xc2x0, an exact position of the film member can be directly detected by the potentiometer so that the film member is moved at a pre-set position. Thus, a low-priced DC motor can be employed for the air passage controlling system instead of a high-priced step motor, resulting in cost reduction of the air passage controlling system.
Preferably, the potentiometer is attached to the first shaft at a side opposite to a side of the electric motor in an axial direction of the first shaft. Alternatively, the electric motor is attached to the first shaft, and the potentiometer is attached to the second shaft. Thus, the potentiometer can be readily provided in a limited small space to reduce the size of the air passage controlling system.